Thanks, gals. I have a heart rate monitor and have only just begun to use it. But I do remember intervals back from my running days. I came to road biking via Spinning class, so we did intervals there and worked on spinning. I probably should work on my pedalling technique. When I concentrate on it, I automatically go faster with less effort.

Thanks for the training book suggestions too. I'll definitely check those out! My goal right now is to complete El Tour de Tucson in November (109 miles), but the goal I have in the back of my mind is to finish in 7 hours, which is averaging 15.6 mph for the whole event, including stops. I know I can do it, but having a good training program will be key.